(1) Field of the Invention
The present invention relates to a breathing apparatus for diving, of the type comprising a breathing bag, a mouthpiece, inhaling and exhaling ducts connected to the bag and to the mouthpiece, these inhaling and exhaling ducts being respectively provided with inhaling and exhaling non return valves and a so called "drainage device".
(2) Description of Prior Art
Depending on the use requirements, a breathing apparatus comprises, either one or more bottle(s) of a gas mixture comprising an exact proportion of oxygen and inert gas, for example nitrogen, or one or more bottle(s) of inert gas or gas mixture.
In the latter case, the breathing apparatus comprises means for introducing a suitable proportion of oxygen and inert gas in the bag.
This arrangement is well known and operates in response to the following use requirements.
In such apparatus the partial pressure of the oxygen contained in the mixture inhaled from the bag must remain substantially constant or more specifically should range between two extreme values, called security values, for example between 0.2 bar and 2 bars. This is intended for the safety of the diver, whatever the oxygen consumption, which may for example be between 0.5 l/min. and 2 l/min.
It is therefore absolutely necessary to provide for a concentration of oxygen in the inhaled mixture, which is smaller as depth increases, and consequently the surrounding pressure is itself larger.
The devices of the prior art which operate with a breathing bag and either a bottle comprising a mixture adapted to the zone of the working depths, or a bottle of oxygen and one or more bottle(s) of inert gas with means for mixing the oxygen and the inert gas in a proportion adapted to the depth at which the diver works, meet this requirement.
Such a breathing apparatus should also enable to ensure the following requirement. It is known that the diver absorbs a mixture of oxygen and inert gas and returns a portion containing less oxygen and carbon dioxide , When this return takes place directly in water, there are two well known disadvantages:
there is a waste of gas which could be reused,
the gas return in water produces bubbles and renders the presence of the diver relatively detectable.
In a manner well known to those skilled in the art, these disadvantages may be overcome by returning the gas to the breathing bag, from which a fraction of the gas previously returned could be reinhaled, and by incorporating the drainage device in the breathing apparatus, the draining device being adapted to permit rejection of a fraction of the volume of the exhaled gas in water. For example, when diving down, the diver can engage the drainage device, which enables him to reach great depths, by remaining, as regards partial pressure of oxygen, between two extreme safety values, while rejecting only a small portion of the volume of exhaled gas, which produces a condition whereby the diver is relatively unnoticed. As soon as the diver has reached a depth area in which he intends to work and circulate, he can bypass the drainage device and thereby work in closed circuit where there is no rejection of exhaled gas.
Experience and research in the field of skin or scuba diving has indicated that in order to have a good compromise in the rate of oxygen equilibrium in the breathing bag, a relative calm environment when the drainage device is engaged and a consumption of gas, such as inert gas, which is minimized, the fraction of the exhaled gas which is rejected in water should be of the order of 1/10 to 1/15 of the inhaled gas.
A drainage device is described in French patent No. 1,538,952. According to this patent, the apparatus comprises a compressible drainage bag whose volume corresponds to a predetermined fraction (for example 1/12) of the breathing bag, and which is connected thereto. The apparatus also comprises means for filling, when exhaling, the drainage bag essentially with an inert gas, and when inhaling for emptying a good portion of this bag. In this manner, the quantity of gas previously exhaled, and rejected in water during the cycle following inhaling, substantially corresponds, in this example, to 1/12 of the gas inhaled during this inhaling cycle.
This purely mechanical device gives a particularly reliable operation of the entire breathing apparatus. Unfortunately, this device has the disadvantages that it is difficult to operate and to manufacture, and moreover it is particularly cumbersome.
Purely electronic control devices have also been proposed, which essentially consist of means for analyzing the partial pressure of oxygen in the bag, and means to control the means the required quantity of oxygen in the bag.
These devices obviously overcome some of the disadvantages mentioned above, they are seriously deficient due to the fact that the safety of the diver is directly dependent on the good operation of these electronic devices and therefore on their reliability.